Expansion anchors can be used to secure selected objects to any sedimentary material such as stone or other masonry; however, an important use of such apparatus is to support the roof of a mine. The roof of a mine shaft is supported by drilling a series of bores in the stratum forming the roof of the mine. Roof straps or roof plates usually constructed of iron or steel are then connected to the roof by inserting elongated mine roof support bolts carrying expansion shells through apertures formed in the roof straps or plates and inserting the expansion shells into the predrilled bores. The mine roof support bolts typically have a head on a lower end thereof or provide for the attachment of a nut thereon to support the roof strap or plate subjacent the roof. Once the expansion shells are received in the predrilled bore they are expanded using apparatus and methods described hereafter to engage and grip the surfaces of the stratum forming the bore thus securing the shell therein. Depending on the apparatus used, the roof strap or plate may be tightened in pressed abutment with the roof as the expansion shell is secured within the predrilled bore or at some time thereafter.
U.S. Pat. No. 1,244,992 issued to Lee on Oct. 30, 1917, discloses an expansion bolt having a flared end and an elongated shaft. The bolt is inserted within a predrilled bore with the flared end being inserted first. A cutting sleeve having a plurality of fingers is inserted within the bore and around the shaft to slide thereon in contact with the flared end. The sleeve is manually driven by repetitive impacts from a driving tool to wedge between the flared end and the wall in which the bore was drilled thereby securing the sleeve and the bolt within the bore. A nut threadably connected to the shaft is used to connect a flange or other object to the bolt and thus to the wall.
U.S. Pat. No. 3,941,028 issued to Lobello et al. on Mar. 2, 1976 discloses an expansion anchor having a threaded bolt with a head on a lower end thereof. A gripping element having a plurality of upwardly extending fingers is connected to the bolt by a lower nut threadably connected to the bolt. Rotation of the bolt urges a tapered nut downward to press the fingers laterally and into the stratum in which the anchor is received. The fingers have ridges thereon that grip the stratum thus inhibiting removal of the anchor. Similar apparatus are disclosed in U.S. Pat. Nos. 3,964,229 and 4,400,122 issued to Fischer and Minnaar et al. respectively.
U.S. Pat. No. 4,789,284 issued to White on Dec. 6, 1988 discloses a self-cutting expansion anchor including an elongated bolt having a head on a lower end thereof. A thrust nut is threadably connected to a lower portion of the bolt and supports a cutting and expanding mechanism having a pair of upwardly extending fingers with cutting blades on the upper ends thereof. A ramp nut is threadably connected to an upper portion of the bolt having tapered grooves therein which receive the cutting finger. A destructible plug received within the ramp plug temporarily secures the ramp plug in non-rotational relation to the elongated bolt. Rotation of the bolt rotates the ramp nut and cutting fingers thereby causing the cutting blades to circumferentially cut and expand the bore in which the expansion anchor is received. The thrust nut urges the cutting fingers upwardly and outwardly during the cutting process. Stops connected to the fingers will eventually contact the walls of the bore and stop the rotation of the fingers and the ramp nut. Continued rotation of the bolt will disintegrate the destructible plug and urge the ramp nut downward to press the fingers against the walls of the expanded bore.
Of the aforecited art, Lobello et al., Fischer and Minnaar et al. do not provide apparatus for expanding the diameter of the bore. Such expansion is a crucial component in maximizing the gripping capacity of an expansion anchor.
Lee provides apparatus for expanding the diameter of the bore but does not provide apparatus for exerting radial pressure on the sleeve after the sleeve has been driven into the bore. The sleeve dislodges a portion of the wall forming the bore and when driven therein, fills the void left by the dislodged portions of the wall; however, without additional radial pressure exerted on the sleeve, the sleeve could be susceptible to slippage. Lee requires several steps to complete connection of the selected object to the wall. The bolt must be inserted within the bore, the sleeve manually fitted over the shaft and driven into the bore, the driving tool disconnected from the sleeve and the selected object connected to the bolt with a nut. Repetitive use of the expansion bolt disclosed in Lee would require a substantial amount of manpower work hours resulting in significant expense to the cost of operating the mine.
White provides an expansion anchor that exerts additional radial force against the cutting blades once the blades have circumferentially cut a predetermined conical notch in the diameter of the bore. Furthermore, White provides an expansion anchor that will connect a roof strap in two easy steps, insertion of the anchor within the bore and rotation of the bolt head. Though very effective for the purpose intended, White is limited to use in relatively soft rock formations. The circumscriptive cutting action of the blades must meet little resistance as over exertion on the blades will disintegrate the destructible plug thereby terminating the rotation of the cutting fingers. Furthermore, the thrust nut can only move upwardly if the rock formation is soft enough to permit the stop members connected to the thrust nut and the cutting fingers to gouge a vertical furrow through the rock formation.